As the demand for high performance microelectronic devices increases, there is a continued need for more compact, higher speed integrated circuit devices such as bipolar transistors. Moreover, there is a continued need for high performance integrated circuit contacts to these devices which do not degrade the inherent performance of the high speed, compact devices.
Compact devices with high speed performance may be fabricated using "self-aligned" processes. In a self-aligned process, at least one device region is used as an alignment guide for forming a second region, thereby eliminating or reducing alignment registration errors produced by equipment tolerances. Examples of integrated circuit bipolar transistors formed by self-aligned processes may be found in U.S. Pat. No. 4,927,774 to Welbourn et al. entitled Self Aligned Bipolar Fabrication Process; in a publication entitled High Speed Bipolar ICs Using Super Self-Aligned Process Technology to Sakai et al. published in the Japanese Journal of Applied Physics, Vol. 20, Supplement 20-1, pp. 155-159 (1981); and in a publication entitled A 30-ps Si Bipolar IC Using Super Self-Aligned Process Technology to Konaka et al. published in the IEEE Transactions on Electron Devices, Vol. ED-33, No. 4, pp. 526-531, April 1986. Many other examples of self-aligned bipolar transistor fabrication processes may be found.
Operating speed of bipolar transistors may also be improved by reducing the parasitic components within the device. Typically, the most significant parasitic components include the base-collector capacitance, the emitter-base capacitance, the collector to substrate capacitance and the base resistance. In order to reduce the parasitic components, virtually all high speed integrated circuit bipolar transistors use heavily doped polycrystalline silicon (polysilicon) to form the base contact, also referred to as the "extrinsic base", and the emitter contacts of the devices. The polysilicon base contact and emitter contact are typically isolated from one another using a silicon oxide layer thermally grown from the polysilicon. Examples of bipolar transistors using polysilicon contacts are found in U.S. Pat. No. 3,600,651 to Duncan entitled Bipolar and Field-Effect Transistor Using Polycrystalline Epitaxial Deposited Silicon; U.S. Pat. No. 4,495,010 to Kranzer entitled Method for Manufacturing Fast Bipolar Transistors; U.S. Pat. No. 4,523,370 to Sullivan et al. entitled Process for Fabricating a Bipolar Transistor with a Thin Base and an Abrupt Base-Collector Junction; and U.S. Pat. No. 4,933,737 to Nakamura et al. entitled Polysilicon Contacts to IC Mesas; and in a publication entitled A Self-Aligning Polysilicon EIectrode Technology (SPEL) for Future LSIS to Misawa et al. published in IEDM 87 pp. 32-35 (1987).
Unfortunately, when using polysilicon base and emitter contacts, the extrinsic base and emitter resistances are dependent upon the quality of the polysilicon material. As is well known to those having skill in the art, it is difficult to obtain high quality polysilicon material because of the difficulty in controlling grain size, impurity diffusion, resistivity and oxide trapping. Similarly, the integrity and long term stability of the polysilicon base and emitter contact regions is dependent upon the formation of reproducible, low-leakage polysiliconoxide insulators. In addition, polysilicon has a much lower carrier mobility, and therefore a larger resistance, than does single crystal silicon.
Attempts have been made to substitute monocrystalline (single crystal) silicon for polysilicon in bipolar transistors to improve the performance thereof. For example, IBM Technical Disclosure Bulletin Vol. 28, No. 1, June 1985 pages 200-201 entitled Substitution of Single Crystalline Silicon for Polysilicon in Transistor Manufacture, describes a single crystal silicon base contact. An article by S.J. Duey and coinventor G. W. Neudeck entitled A Novel Quasi-Dielectrically Isolated Bipolar Transistor Using Epitaxial Lateral Overgrowth, IEEE 1988 Bipolar Circuits and Technology Meeting, page 241, describes a power bipolar transistor which uses epitaxial lateral overgrowth to form a transistor which has a monocrystalline collector contact. Emitter and base contacts are not included. Rather, the emitter and base directly contact the emitter and base electrodes. Junction isolation is used to isolate the base and emitter and the emitter and collector.
In summary, the art has yet to produce a compact integrated circuit bipolar transistor which includes monocrystalline contacts for the base, emitter and collector. The art has also not provided a self-aligned process for forming such a transistor.